Semiconductor memory device

ABSTRACT

According to one embodiment, a semiconductor memory device includes a plurality of first interconnects extending in a first direction, a plurality of second interconnects extending in a second direction crossing the first direction, and a memory element provided between the first interconnect and the second interconnect at a portion where the first interconnect crosses the second interconnect. The memory element includes a variable resistance film and a stress generating film stacked with the variable resistance film to apply stress to the variable resistance film in a surface direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromU.S. Provisional Patent Application 61/803,512, filed on Mar. 20, 2013;the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor memorydevice.

BACKGROUND

A resistance change element has been proposed as a memory cell of a newnonvolatile semiconductor memory device. A variable resistance film canbe switched to at least two resistance states having relativelydifferent resistances by controlling the magnitude, polarity, andapplication time of the voltage applied to the variable resistance film,etc.

For example, an ion-movement type resistance change element has beenproposed in which the resistance is changed by causing metal ions and/oroxygen ions inside the variable resistance film to move by an appliedvoltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing an example of a memorycell array of a semiconductor memory device of a first embodiment;

FIG. 2A to FIG. 5C are schematic cross-sectional views showing anexample of a memory element of the semiconductor memory device of thefirst embodiment;

FIG. 6 is a schematic perspective view showing an example of a memorycell array of a semiconductor memory device of a second embodiment; and

FIG. 7A to FIG. 8B are schematic cross-sectional views showing anexample of a memory element of the semiconductor memory device of thesecond embodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor memory device includes aplurality of first interconnects extending in a first direction, aplurality of second interconnects extending in a second directioncrossing the first direction, and a memory element provided between thefirst interconnect and the second interconnect at a portion where thefirst interconnect crosses the second interconnect. The memory elementincludes a variable resistance film and a stress generating film stackedwith the variable resistance film to apply stress to the variableresistance film in a surface direction.

Various embodiments will be described hereinafter with reference to theaccompanying drawings. Similar components in the drawings are markedwith like reference numerals.

First Embodiment

FIG. 1 is a schematic perspective view of an example of a memory cellarray 1 in a semiconductor memory device of a first embodiment.

The memory cell array 1 includes multiple first interconnects 11 andmultiple second interconnects 12. Further, the memory cell array 1includes stacked films 10 having columnar configurations providedbetween the first interconnects 11 and the second interconnects 12.

The first interconnects 11 and the second interconnects 12 cross eachother three-dimensionally to be non-parallel. For example, the firstinterconnects 11 extend in a first direction (a Y direction); the secondinterconnects 12 extend in a second direction (an X direction)orthogonal to the first direction; and the first interconnects 11 andthe second interconnects 12 are orthogonal to each other. Each of themultiple stacked films 10 is provided at a cross point where the firstinterconnect 11 and the second interconnect 12 cross each other.

The multiple stacked films 10 are disposed in two-dimensional directions(XY directions) in, for example, a matrix configuration; and an arrayhaving the matrix configuration is multiply stacked in a third direction(a Z direction) orthogonal to the XY plane.

FIG. 1 shows, for example, a portion in which 4 layers of an array of 3rows by 3 columns are stacked.

The first interconnect 11 is shared by the stacked films 10 on and underthe first interconnect 11. Similarly, the second interconnect 12 isshared by the stacked films 10 on and under the second interconnect 12.

The stacked film 10 includes a memory element (a memory cell).

FIG. 2A is a schematic cross-sectional view showing an example of thememory element.

The memory element includes a lower layer electrode 21, an upper layerelectrode 22, and a variable resistance film 20 that is provided betweenthe lower layer electrode 21 and the upper layer electrode 22.

The variable resistance film 20 is stacked on the lower layer electrode21; and the lower layer electrode 21 contacts the lower surface of thevariable resistance film 20.

The upper layer electrode 22 is stacked on the variable resistance film20 to contact the upper surface of the variable resistance film 20.

The variable resistance film 20 is electrically switchable between astate (a set state) in which the resistance is relatively low and astate (a reset state) in which the resistance is relatively high tononvolatilely store data.

The variable resistance film 20 includes a metal oxide. For example, thevariable resistance film 20 includes an oxide of at least one elementselected from lithium (Li), manganese (Mn), tantalum (Ta), niobium (Nb),chromium (Cr), nickel (Ni), tungsten (W), cobalt (Co), iron (Fe),hafnium (Hf), titanium (Ti), silicon (Si), and zirconium (Zr).

The variable resistance film 20 in the low resistance state (the setstate) which has a relatively low resistance can be switched to the highresistance state (the reset state) which has a relatively highresistance when a reset voltage is applied to the variable resistancefilm 20 via the interconnects 11 and 12 on and under the memory elementsubjected to the operation. The variable resistance film 20 can beswitched to the low resistance state (the set state) when a set voltagethat is higher than the reset voltage is applied to the variableresistance film 20 in the high resistance state (the reset state).

According to the embodiment, the resistance value is changed byelectrically causing metal ions and/or oxygen ions inside the variableresistance film 20 to move. Such an ion-movement type resistance changeelement is largely considered to have two improvement points due to thematerial of the variable resistance film 20.

One point is that, because the ions move easily, even in the case whereprogramming using the ion movement is performed, there is a highprobability of the ions returning to the original positions; and thedata retention characteristics degrade.

One other point is that the ions do not move easily; and the number ofpossible reads and programs decreases due to the ions undesirably movingwhile damaging the crystal of the main material.

It is considered that the former occurs because the paths of the ionsinside the crystal of the main material are sufficiently large for thesize of the ions; and the ions unfortunately can move easily.

It is considered that the latter occurs because the paths of the ionsare so small that the crystal of the main material is undesirablydamaged.

In either case, it is difficult to realize both a sufficient number ofprograms and a sufficient retention time of data.

For example, the variable resistance film 20 of the embodiment includesmainly LiCoO₂, LiMn₂O₄, LiNiO₂, LiFePO₄, etc., as the metal oxide.

The resistance of the variable resistance film 20 is changed by causingthe Li ions to move to the lower layer electrode 21 vicinity and/or theupper layer electrode 22 vicinity by applying a voltage between theupper and lower electrodes 22 and 21.

However, because it is possible for the Li ions inside the Li oxide filmto move easily, the Li ions easily return to the original positions whenthe voltage application is stopped.

Therefore, according to the embodiment, the lattice constant of the mainmaterial crystal of the variable resistance film 20 is adjusted byapplying stress to the variable resistance film 20.

For example, in the example shown in FIG. 2A, compressive stress isapplied to the variable resistance film 20 by stacking the upper layerelectrode 22 that has compressive stress on the variable resistance film20.

In the first embodiment, the direction of the stress of each of thefilms is the surface direction of the film.

The lattice constant in the surface direction of the variable resistancefilm 20 to which the compressive stress is applied by the upper layerelectrode 22 becomes smaller than prior to the compressive stress beingapplied, that is, prior to forming the upper layer electrode 22. Whenthe upper layer electrode 22 is peeled after forming the upper layerelectrode 22, the compressive stress that had been applied to thevariable resistance film 20 from the upper layer electrode 22 isrelaxed; and the lattice constant in the surface direction of thevariable resistance film 20 becomes larger than that of the state inwhich the upper layer electrode 22 was stacked on the variableresistance film 20.

The variable resistance film 20 itself may not have compressive stress.Even in the case where the variable resistance film 20 has tensilestress, the tensile stress of the variable resistance film 20 becomessmaller than prior to forming the upper layer electrode 22 by theformation of the upper layer electrode 22 that has compressive stress;and it is possible to reduce the lattice constant.

The change of the lattice constant (the lattice strain) can be analyzedby, for example, Nano Beam Electron Diffraction to obtain an electrondiffraction pattern by irradiating a nanobeam having a diameter ofseveral tens of nm.

By the lattice constant of the variable resistance film 20 becomingsmall, the paths of the Li ions become narrow; and the Li ions move lesseasily.

Thereby, it is possible to stably store the data memory state becausethe Li ions that move due to the voltage application are stored atsubstantially the same positions even after stopping the voltageapplication.

For example, a titanium nitride film formed by sputtering using atitanium target in a nitrogen atmosphere can be used as the upper layerelectrode 22 which is the stress generating film. It is possible togenerate the compressive stress and it is possible to adjust themagnitude of the stress by adjusting the film formation temperature andnitrogen content of the sputtering film formation of the titaniumnitride film, etc. The upper layer electrode 22 is formed to havecompressive stress that is, for example, not less than 1 GPa.

Also, a film other than the electrodes can be used as the stressgenerating film.

FIG. 2B shows the structure of a memory element in which a stressgenerating film 32 is stacked on the upper layer electrode 22.

The stress generating film 32 has compressive stress. The compressivestress of the stress generating film 32 is applied to the upper layerelectrode 22, which is stacked under the stress generating film 32 andis in contact with the stress generating film 32, and is further appliedto the variable resistance film 20 under the upper layer electrode 22.

The lattice constant in the surface direction of the variable resistancefilm 20 to which the compressive stress is applied by the stressgenerating film 32 becomes smaller than prior to the compressive stressbeing applied, that is, prior to forming the stress generating film 32.When the stress generating film 32 is peeled after forming the stressgenerating film 32, the compressive stress that had been applied to thevariable resistance film 20 from the stress generating film 32 isrelaxed; and the lattice constant in the surface direction of thevariable resistance film 20 becomes larger than that of the state inwhich the stress generating film 32 was stacked on the variableresistance film 20.

In such a case as well, the variable resistance film 20 itself may nothave compressive stress. Even in the case where the variable resistancefilm 20 has tensile stress, the tensile stress of the variableresistance film 20 becomes smaller than prior to forming the stressgenerating film 32 by the formation of the stress generating film 32that has compressive stress; and it is possible to reduce the latticeconstant.

By the lattice constant of the variable resistance film 20 becomingsmall, the paths of the Li ions become narrow; the Li ions move lesseasily; and it is possible to stably store the data memory state becausethe Li ions that move due to the voltage application are stored at thesame positions even after stopping the voltage application.

The stress generating film 32 is an insulating film or a conductor film.

The stress generating film 32 is, for example, a silicon nitride film.Compressive stress can be applied to the silicon nitride film and themagnitude of the compressive stress can be adjusted by adjusting thenitrogen content (the nitrogen concentration) and/or film formationtemperature of the silicon nitride film. The stress generating film 32is formed to have, for example, compressive stress that is not less than1 GPa.

Also, as shown in FIG. 2C, compressive stress may be applied to both theupper layer electrode 22 and the lower layer electrode 21; and thecompressive stress can be applied to the variable resistance film 20from both the upper layer electrode 22 and the lower layer electrode 21.The upper layer electrode 22 and the lower layer electrode 21 havecompressive stress that is in the surface direction of the film and inthe same direction.

The lower layer electrode 21 may include the same film as the upperlayer electrode 22, e.g., a titanium nitride film. By performingannealing after forming the variable resistance film 20 on the lowerlayer electrode 21, the compressive stress can be generated in the lowerlayer electrode 21; and the compressive stress can be applied to thevariable resistance film 20 from the lower layer electrode 21.

Also, as shown in FIG. 3A, a structure may be used in which only thelower layer electrode 21 is used as the stress generating film. Byperforming annealing after forming the variable resistance film 20 onthe lower layer electrode 21, the compressive stress can be generated inthe lower layer electrode 21; and the compressive stress can be appliedto the variable resistance film 20 from the lower layer electrode 21.

Further, as shown in FIG. 3B, a structure may be used in which a stackedbody having the variable resistance film 20 interposed between theelectrodes 21 and 22 is interposed between the stress generating film 32and a stress generating film 31.

The lower layer electrode 21 is stacked on the stress generating film31; and the stress generating film 32 is stacked on the upper layerelectrode 22.

The stress generating film 31 on the lower side and the stressgenerating film 32 on the upper side have compressive stress that is inthe surface direction of the film and in the same direction.

The stress generating film 31 and the stress generating film 32 are thesame film, e.g., a silicon nitride film.

Also, as shown in FIG. 3C, the compressive stress may be applied to thevariable resistance film 20 by only the stress generating film 31stacked under the lower layer electrode 21.

By performing annealing after forming the variable resistance film 20 onthe stress generating film 31 with the lower layer electrode 21interposed, the compressive stress can be generated in the stressgenerating film 31; and the compressive stress can be applied from thestress generating film 31 to the variable resistance film 20 via thelower layer electrode 21.

The variable resistance film 20 is not limited to Li oxide and may havea structure including, for example, Mn₃O₄. There is a possibility thatthe crystal of the Mn₃O₄ which is used as the main material may bedamaged when the Mn ions move inside the Mn₃O₄ due to the voltageapplication; and there are cases where the number of possible programsand erases becomes low.

Therefore, when the variable resistance film 20 includes Mn₃O₄, it isfavorable to use a stress generating film that has tensile stress ratherthan compressive stress.

Thereby, it is possible to increase the lattice constant of the variableresistance film 20, widen the paths of the Mn ions, and drasticallyincrease the number of possible programs and erases.

Further, the resistance can be changed by causing the oxygen ions tomove inside the film by a voltage application for the variableresistance film 20 including a metal oxide such as TaOx, NbOx, CrOx,NiOx, WOx, CoOx, FeOx, HfOx, TiOx, SiOx, ZrOx, etc. In these films aswell, the crystal is damaged easily because the paths of the oxygen ionsare small.

Accordingly, it is possible to widen the paths of the oxygen ions anddrastically increase the number of programs and erases by stacking astress generating film that has tensile stress for the variableresistance film 20 in which the movement of the oxygen ions contributesto the resistance change.

In the example shown in FIG. 4A, tensile stress is applied to thevariable resistance film 20 by stacking the upper layer electrode 22that has tensile stress on the variable resistance film 20.

The lattice constant in the surface direction of the variable resistancefilm 20 to which the tensile stress is applied by the upper layerelectrode 22 becomes larger than prior to the tensile stress beingapplied, that is, prior to forming the upper layer electrode 22. Whenthe upper layer electrode 22 is peeled after forming the upper layerelectrode 22, the tensile stress that had been applied to the variableresistance film 20 from the upper layer electrode 22 is relaxed; and thelattice constant in the surface direction of the variable resistancefilm 20 becomes smaller than that of the state in which the upper layerelectrode 22 was stacked on the variable resistance film 20.

The variable resistance film 20 itself may not have tensile stress. Evenin the case where the variable resistance film 20 has compressivestress, the compressive stress of the variable resistance film 20becomes smaller than prior to forming the upper layer electrode 22 bythe formation of the upper layer electrode 22 that has tensile stress;and it is possible to increase the lattice constant.

By the lattice constant of the variable resistance film 20 becominglarge, the paths of the ions widen; and the ions move more easily.

Thereby, the crystal damage due to the movement of the ions can besuppressed; and it is possible to drastically increase the number ofpossible programs and erases.

For example, a titanium nitride film formed by sputtering using atitanium target in a nitrogen atmosphere can be used as the upper layerelectrode 22 which is the tensile stress generating film. By adjustingthe nitrogen content and/or film formation temperature of the titaniumnitride film, it is possible to generate tensile stress in the titaniumnitride film; and it is possible to adjust the magnitude of the tensilestress.

For example, it is possible to change a compressive stress of about 1GPa to a tensile stress of several hundred MPa by reducing the DC powerand by reducing the TiN density in DC (direct current) sputtering.

A film other than the electrodes can be used as the tensile stressgenerating film.

FIG. 4B shows the structure of a memory element in which the stressgenerating film 32 is stacked on the upper layer electrode 22.

The stress generating film 32 has tensile stress. The tensile stress ofthe stress generating film 32 is applied to the upper layer electrode22, which is stacked under the stress generating film 32 and is incontact with the stress generating film 32, and is further applied tothe variable resistance film 20 under the upper layer electrode 22.

The lattice constant in the surface direction of the variable resistancefilm 20 to which the tensile stress is applied by the stress generatingfilm 32 becomes larger than prior to the tensile stress being applied,that is, prior to forming the stress generating film 32. When the stressgenerating film 32 is peeled after forming the stress generating film32, the tensile stress that had been applied to the variable resistancefilm 20 from the stress generating film 32 is relaxed; and the latticeconstant in the surface direction of the variable resistance film 20becomes smaller than that of the state in which the stress generatingfilm 32 was stacked on the variable resistance film 20.

In such a case as well, the variable resistance film 20 itself may nothave tensile stress. Even in the case where the variable resistance film20 has compressive stress, the compressive stress of the variableresistance film 20 becomes smaller than prior to forming the stressgenerating film 32 by the formation of the stress generating film 32that has tensile stress; and it is possible to increase the latticeconstant.

By the lattice constant of the variable resistance film 20 becominglarge, the paths of the ions widen; the ions move more easily; thecrystal damage due to the movement of the ions can be suppressed; and itis possible to drastically increase the number of possible programs anderases.

The stress generating film 32 is an insulating film or a conductor film.

The stress generating film 32 is, for example, a silicon nitride film.By adjusting the nitrogen content (the nitrogen concentration) and/orfilm formation temperature of the silicon nitride film, tensile stresscan be applied to the silicon nitride film; and the magnitude of thetensile stress can be adjusted. The stress generating film 32 is formedto have tensile stress that is, for example, not less than 1 GPa.

Also, as shown in FIG. 4C, the tensile stress can be applied to both theupper layer electrode 22 and the lower layer electrode 21; and thetensile stress can be applied to the variable resistance film 20 fromboth the upper layer electrode 22 and the lower layer electrode 21. Theupper layer electrode 22 and the lower layer electrode 21 have tensilestress that is in the surface direction of the film and in the samedirection.

The lower layer electrode 21 may include the same film as the upperlayer electrode 22, e.g., a titanium nitride film. By performingannealing after forming the variable resistance film 20 on the lowerlayer electrode 21, the tensile stress can be generated in the lowerlayer electrode 21; and the tensile stress can be applied to thevariable resistance film 20 from the lower layer electrode 21.

Further, as shown in FIG. 5A, a structure may be used in which only thelower layer electrode 21 is used as the stress generating film. Byperforming annealing after forming the variable resistance film 20 onthe lower layer electrode 21, the tensile stress can be generated in thelower layer electrode 21; and the tensile stress can be applied to thevariable resistance film 20 from the lower layer electrode 21.

Also, as shown in FIG. 5B, a structure may be used in which a stackedbody having the variable resistance film 20 interposed between theelectrodes 21 and 22 is interposed between the stress generating film 32and the stress generating film 31.

The lower layer electrode 21 is stacked on the stress generating film31; and the stress generating film 32 is stacked on the upper layerelectrode 22.

The stress generating film 31 on the lower side and the stressgenerating film 32 on the upper side have tensile stress that is in thesurface direction of the film and in the same direction.

The stress generating film 31 and the stress generating film 32 are thesame film, e.g., a silicon nitride film.

Also, as shown in FIG. 5C, the tensile stress may be applied to thevariable resistance film 20 by only the stress generating film 31stacked under the lower layer electrode 21.

By performing annealing after forming the variable resistance film 20 onthe stress generating film 31 with the lower layer electrode 21interposed, the tensile stress can be generated in the stress generatingfilm 31; and the tensile stress can be applied from the stressgenerating film 31 to the variable resistance film 20 via the lowerlayer electrode 21.

Second Embodiment

FIG. 6 is a schematic perspective view showing an example of a memorycell array of a semiconductor memory device of a second embodiment.

The memory cell array of the second embodiment is provided on anot-shown substrate and includes multiple variable resistance films 50having tubular configurations extending in the Z direction (firstdirection) perpendicular to a major surface of the substrate.

Here, two directions that are orthogonal to each other in a planeparallel to the major surface of the substrate and orthogonal to the Zdirection are taken as the X direction (second direction) and the Ydirection (third direction).

Center electrodes 52 having columnar configurations extending in the Zdirection are provided inside the variable resistance films 50. Thevariable resistance films 50 are provided at the outer circumferences ofthe center electrodes 52 having the columnar configurations.

The multiple center electrodes 52 and the multiple variable resistancefilms 50 are disposed in a matrix configuration when the major surfaceof the substrate is viewed in plan.

Multiple outer electrodes 51 are multiply arranged in the X direction tobe disposed between the center electrodes 52. Here, the outer electrodes51 are provided between the variable resistance films 50 that areadjacent to each other in the X direction; and the outer electrodes 51are shared by the variable resistance films 50 that are adjacent to eachother in the X direction.

The outer electrodes 51 extend in the Y direction. Here, the outerelectrodes 51 are shared by the variable resistance films 50 of thecenter electrodes 52 that are adjacent to each other in the Y direction.Also, the outer electrodes 51 are stacked in the Z direction with anot-shown inter-layer insulating film interposed.

The variable resistance film 50 includes a metal oxide. The variableresistance film 50 includes, for example, an oxide of at least oneelement selected from lithium (Li), manganese (Mn), tantalum (Ta),niobium (Nb), chromium (Cr), nickel (Ni), tungsten (W), cobalt (Co),iron (Fe), hafnium (Hf), titanium (Ti), silicon (Si), and zirconium(Zr).

When a voltage is applied to the center electrode 52 and the outerelectrode 51, the ions of the region of the variable resistance film 50interposed between the center electrode 52 and the outer electrode 51move; the resistance of the region changes; and the programming anderasing of data are performed.

Two data can be stored by two outer electrodes 51 of the same layerbeing disposed at one center electrode 52 with the variable resistancefilm interposed in the X direction.

In the second embodiment as well, stress is applied to the variableresistance film 50.

FIG. 7A is a schematic cross-sectional view of one variable resistancefilm 50 and a pair of outer electrodes 51 having the variable resistancefilm 50 interposed in the X direction and corresponds to a cross sectionparallel to the XY plane of FIG. 6.

For example, the variable resistance film 50 includes mainly LiCoO₂,LiMn₂O₄, LiNiO₂, LiFePO₄, etc., as the metal oxide.

In the example shown in FIG. 7A, stress is applied to the variableresistance film 50 by generating stress in the center electrode 52 thatis provided in the columnar configuration inside the variable resistancefilm 50.

In the second embodiment, the direction of the stress of the stressgenerating film having the columnar configuration is the centraldirection; and the direction of the stress of the variable resistancefilm 50 having the tubular configuration is the circumferentialdirection.

Compressive stress that is in the circumferential direction or the Ydirection is generated in the center electrode 52 that is used as thestress generating film at the portion opposing the outer electrode 51with the variable resistance film 50 interposed. The compressive stressis applied to the portion of the variable resistance film 50 that isinterposed between the outer electrode 51 and the center electrode 52.

Thereby, the lattice constant in the circumferential direction or the Ydirection of the variable resistance film 50 at the portion interposedbetween the outer electrode 51 and the center electrode 52 becomessmaller than prior to the compressive stress being applied, that is,prior to forming the center electrode 52. When the center electrode 52is removed, the compressive stress that had been applied to the variableresistance film 50 from the center electrode 52 is relaxed; and thelattice constant in the circumferential direction or the Y direction ofthe variable resistance film 50 at the portion interposed between theouter electrode 51 and the center electrode 52 becomes larger than thatof the state in which the center electrode 52 had been formed.

By the lattice constant of the variable resistance film 50 at theportion interposed between the outer electrode 51 and the centerelectrode 52 becoming small, the paths of the Li ions become narrow; andthe Li ions move less easily.

Thereby, it is possible to stably store the data memory state becausethe Li ions that move due to the voltage application are stored at thesame positions even after stopping the voltage application.

After making multiple holes in a stacked body on the substrate to extendin the Z direction, the variable resistance film 50 is formed in tubularconfigurations at the inner circumferential walls of the holes.

Continuing, the center electrode 52 is formed as a film inside thevariable resistance film 50. For example, a titanium nitride film formedby sputtering using a titanium target in a nitrogen atmosphere can beused as the center electrode 52 which is the stress generating film.

Then, in the example shown in FIG. 7B, a center electrode 62 is providedin a tubular configuration inside the variable resistance film 50; and astress generating film 53 having a columnar configuration extending inthe Z direction is provided inside the center electrode 62.

The direction of the stress of the stress generating film 53 having thecolumnar configuration is the central direction. The stress is appliedto the center electrode 62, and is further applied as compressive stressto the portion of the variable resistance film 50 interposed between theouter electrode 51 and the center electrode 52.

Thereby, the lattice constant in the circumferential direction or the Ydirection of the variable resistance film 50 at the portion interposedbetween the outer electrode 51 and the center electrode 52 becomessmaller than prior to the compressive stress being applied, that is,prior to forming the stress generating film 53. When the stressgenerating film 53 is removed, the stress that had been applied to thevariable resistance film 50 from the stress generating film 53 isrelaxed; and the lattice constant in the circumferential direction orthe Y direction of the variable resistance film 50 at the portioninterposed between the outer electrode 51 and the center electrode 52becomes larger than that of the state in which the stress generatingfilm 53 had been formed.

By the lattice constant of the variable resistance film 50 at theportion interposed between the outer electrode 51 and the centerelectrode 52 becoming small, the paths of the Li ions become narrow; andthe Li ions move less easily.

Thereby, it is possible to stably store the data memory state becausethe Li ions that move due to the voltage application are stored at thesame positions even after stopping the voltage application.

After making multiple holes in a stacked body on the substrate to extendin the Z direction, the variable resistance film 50 is formed in tubularconfigurations at the inner circumferential walls of the holes.

Continuing, the center electrode 62 is formed in tubular configurationsat the inner circumferential walls of the variable resistance film 50.

Continuing, the stress generating film 53 is formed inside the centerelectrode 62.

The stress generating film 53 is an insulating film or a conductor film.The stress generating film 53 is, for example, a silicon nitride film.

Also, similarly to the first embodiment, it is possible to widen thepaths of the ions and drastically increase the number of programs anderases by applying tensile stress in the circumferential direction orthe Y direction to the portion of the variable resistance film 50 thatincludes an oxide of at least one element selected from manganese,tantalum, niobium, chromium, nickel, tungsten, cobalt, iron, hafnium,titanium, silicon, and zirconium and is between the outer electrode 51and the center electrode 52.

In the example shown in FIG. 8A, stress is applied to the variableresistance film 50 by generating stress in the center electrode 52 thatis provided in a columnar configuration inside the variable resistancefilm 50 to cause the center electrode 52 to expand in the outercircumferential direction.

Tensile stress is generated in the circumferential direction or the Ydirection in the center electrode 52 that is used as the stressgenerating film at the portion opposing the outer electrode 51 with thevariable resistance film 50 interposed. The tensile stress is applied tothe portion of the variable resistance film 50 interposed between theouter electrode 51 and the center electrode 52.

Thereby, the lattice constant in the circumferential direction or the Ydirection of the variable resistance film 50 at the portion interposedbetween the outer electrode 51 and the center electrode 52 becomeslarger than prior to the tensile stress being applied, that is, prior toforming the center electrode 52. When the center electrode 52 isremoved, the tensile stress that had been applied to the variableresistance film 50 from the center electrode 52 is relaxed; and thelattice constant in the circumferential direction or the Y direction ofthe variable resistance film 50 at the portion interposed between theouter electrode 51 and the center electrode 52 becomes smaller than thatof the state in which the center electrode 52 had been formed.

By the lattice constant of the variable resistance film 50 at theportion interposed between the outer electrode 51 and the centerelectrode 52 becoming large, the paths of the ions widen; and the ionsmove more easily.

Thereby, the crystal damage due to the movement of the ions can besuppressed; and it is possible to drastically increase the number ofpossible programs and erases.

Then, in the example shown in FIG. 8B, the center electrode 62 isprovided in a tubular configuration inside the variable resistance film50; and the stress generating film 53 having a columnar configurationextending in the Z direction is provided inside the center electrode 62.

Stress is generated in the stress generating film 53 having the columnarconfiguration to cause the stress generating film 53 to expand in theouter circumferential direction. The stress is applied to the centerelectrode 62 and is further applied as tensile stress to the portion ofthe variable resistance film 50 interposed between the outer electrode51 and the center electrode 52.

Thereby, the lattice constant in the circumferential direction or the Ydirection of the variable resistance film 50 at the portion interposedbetween the outer electrode 51 and the center electrode 52 becomeslarger than prior to the tensile stress being applied, that is, prior toforming the stress generating film 53. When the stress generating film53 is removed, the tensile stress that had been applied to the variableresistance film 50 from the stress generating film 53 is relaxed; andthe lattice constant in the circumferential direction or the Y directionof the variable resistance film 50 at the portion interposed between theouter electrode 51 and the center electrode 52 becomes smaller than thatof the state in which the stress generating film 53 had been formed.

By the lattice constant of the variable resistance film 50 at theportion interposed between the outer electrode 51 and the centerelectrode 52 becoming large, the paths of the ions widen; and the ionsmove more easily.

Thereby, the crystal damage due to the movement of the ions can besuppressed; and it is possible to drastically increase the number ofpossible programs and erases.

According to the embodiments described above, stress is applied to thevariable resistance film; and the lattice constant of the variableresistance film is adjusted appropriately according to the main materialcrystal and/or type of the mobile ions of the variable resistance film.Thereby, the decrease of the number of possible programs and erases dueto the damage of the main material crystal due to the ion movementinside the variable resistance film or the degradation of the dataretention characteristics due to the ease of the ion movement inside thevariable resistance film can be suppressed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor memory device, comprising: aplurality of first interconnects extending in a first direction; aplurality of second interconnects extending in a second directioncrossing the first direction; and a memory element provided between thefirst interconnect and the second interconnect at a portion where thefirst interconnect crosses the second interconnect, the memory elementincluding: a variable resistance film; and a stress generating filmstacked with the variable resistance film to apply stress to thevariable resistance film in a surface direction.
 2. The semiconductormemory device according to claim 1, wherein the stress generating filmis an electrode stacked on or under the variable resistance film tocontact the variable resistance film.
 3. The semiconductor memory deviceaccording to claim 2, wherein the electrode is a titanium nitride film.4. The semiconductor memory device according to claim 1, wherein thememory element includes: a lower layer electrode; the variableresistance film stacked on the lower layer electrode; and an upper layerelectrode stacked on the variable resistance film.
 5. The semiconductormemory device according to claim 4, wherein the stress generating filmis the upper layer electrode and the lower layer electrode, and theupper layer electrode and the lower layer electrode have stress in asame direction.
 6. The semiconductor memory device according to claim 5,wherein the upper layer electrode and the lower layer electrode aretitanium nitride films.
 7. The semiconductor memory device according toclaim 4, wherein the stress generating film is stacked on the upperlayer electrode or under the lower layer electrode.
 8. The semiconductormemory device according to claim 7, wherein the stress generating filmis a silicon nitride film.
 9. The semiconductor memory device accordingto claim 4, wherein the stress generating film is stacked under thelower layer electrode and on the upper layer electrode, the stressgenerating film stacked under the lower layer electrode and the stressgenerating film stacked on the upper layer electrode have stress in asame direction.
 10. The semiconductor memory device according to claim9, wherein the stress generating film is a silicon nitride film.
 11. Thesemiconductor memory device according to claim 1, wherein the variableresistance film includes lithium oxide.
 12. The semiconductor memorydevice according to claim 11, wherein the stress generating film hascompressive stress.
 13. The semiconductor memory device according toclaim 1, wherein the variable resistance film includes an oxide of atleast one element selected from manganese, tantalum, niobium, chromium,nickel, tungsten, cobalt, iron, hafnium, titanium, silicon, andzirconium.
 14. The semiconductor memory device according to claim 13,wherein the stress generating film has tensile stress.
 15. Asemiconductor memory device, comprising: a variable resistance filmhaving a tubular configuration extending in a first direction; aplurality of outer electrodes provided with the variable resistance filminterposed in a second direction crossing the first direction, theplurality of outer electrodes extending in a third direction crossingthe first direction and the second direction; and a stress generatingfilm provided inside the variable resistance film to apply stress to thevariable resistance film in a circumferential direction.
 16. Thesemiconductor memory device according to claim 15, wherein the stressgenerating film is a center electrode having a columnar configurationprovided inside the variable resistance film to extend in the firstdirection.
 17. The semiconductor memory device according to claim 16,wherein the center electrode is a titanium nitride film.
 18. Thesemiconductor memory device according to claim 15, further comprising acenter electrode having a tubular configuration provided inside thevariable resistance film to extend in the first direction, the stressgenerating film being provided inside the center electrode to extend ina columnar configuration in the first direction.
 19. The semiconductormemory device according to claim 18, wherein the stress generating filmis a silicon nitride film.
 20. The semiconductor memory device accordingto claim 15, wherein the variable resistance film includes a metaloxide.